This invention relates to surveillance systems. More specifically, the invention depicts a method and apparatus to supplement vehicle surveillance systems by providing vehicle identification and position aiding.
The Federal Aviation Administration (FAA) has installed Airport Surface Detection Equipment (ASDE) primary radar systems at the nations busiest airports. These radars provide a display in the Air Traffic Control (ATC) tower cab of runway/taxiway traffic movement. The display provides the tower controllers with enhanced situational awareness when visibility conditions make maintaining direct visual contact with traffic on the airport surface difficult. There are three key deficiencies associated with the ASDE primary radar: (1) surveillance coverage gaps result when radar installations do not have line-of-sight between the radar and the monitored traffic as is the case for complex airport layouts; (2) false targets are generated on the tower displays when multipath interference occurs and (3) primary radar cannot provide identification of aircraft with flight identification (ID).
In an effort to augment ASDE surveillance and resolve deficiencies, the FAA conducted trials of Aircraft Target Identification System (ATIDS) as described in an article titled "Positive Identification of Aircraft on Airport Movement Area--Results of FAA Trials" published in IEEE Aerospace and Electronic Systems Magazine, June 1996. ATIDS uses 1090 MHz multilateration to determine the location of Mode S and Mode A/C transponder equipped aircraft. Similar research using 1090 MHz multilateration is documented in "Station Arrangement Effects on Ground-Referenced Aircraft Height Computation Based on Time Difference of Arrival", published in Navigation: Journal of The Institute of Navigation, Vol. 42, No. 2, Summer 1995 and in "The Czech Passive Surveillance System for Air Traffic Control" published in the Journal of ATC, January-March 1997. The system also decodes aircraft transponder transmissions to determine each aircraft's 4096 code. ATIDS system elements in the ATC tower use the 4096 code to look up the flight ID available through an interface with Automated Radar Tracking System (ARTS). The FAA has demonstrated that the ATIDS position/Flight ID information can be fused with ASDE surveillance. However, one of the major limitations of ATIDS is that Mode S and Mode A/C transmissions are highly susceptible to multipath interference resulting from reflections off airport structures. Multipath interference results in corrupted 1090 MHz receptions at the ATIDS receive stations. Techniques have been developed to aid in the recovery of corrupted transmissions, for example, U.S. Pat. No. 5,528,244 describes a technique for recovering Mode S and Mode A/C transmissions that was tested in the ATIDS test trials. Even with the application of multipath mitigation techniques, reception performance can be significantly low in high multipath environments as was experienced in the ATIDS test trials. Multilateration using the Time Difference of Arrival (TDOA) technique requires reception from a minimum of 3 receivers to determine a 2D position as described in U.S. Pat. No. 5,191,342. To ensure a minimum of three receptions for each transponder transmission, diversity using more than three receivers is required to guarantee the surveillance update success rates required for the surface surveillance application. The cost of additional receivers beyond the minimum of 3 results in increased ATIDS system costs.
Accordingly, what is needed is a new method for performing multilateration that uses two receivers to provide identification of vehicles and provide a 2D position when reception is only available from two multilateration system receivers.